The Clinical Program Core will provide tissue material from surgically excised specimens from women with primary breast cancer. The tissue will include a portion of the tumor, benign appearing breast tissue, skin and, when available, metastatic disease in lymph nodes. Special care will be taken to utilize tissue in an optimal way so that small tumors (~1 cm in diameter) can be included in the study without jeopardizing morphologic diagnosis. This will be achieved by using optimal dissection techniques and continuous updating of the tissue needs of the various research projects. The core will do the initial processing, including in vitro BrdUrd incorporation for study of proliferation and distribution of tissue to the projects. Patients suitable for the in vivo BrdUrd protocol will be identified, prepared, and administered the drug. Blood from patients with breast cancer, and from their parents, when feasible and possible, will be taken for cytogenetic studies. The clinical core will also conduct detailed histologic analyses of all cases and enter the resulting data into the database.